Induction coil design for portable induction heating tool and method for its use

ABSTRACT

A portable induction tool is provided for soldering or brazing sections of metal pipe together. A work coil head (with induction coil) is U-shaped, allowing placement of the head around lengths of pipe, heating a susceptor (e.g., the pipe) to form a joint, and then to be withdrawn after the pipe joint is made. In one form, the tool uses heat pipes to remove thermal energy from the head, and also a heat exchanger for higher-powered units. Power capacitors are generally included with the induction (work) coil to create a tank circuit of a resonant frequency. The induction coil uses Litz wire, copper tubing, or heat pipes with a conductive outer skin to carry the high-current being delivered to the induction coil. The induction coil has a general racetrack configuration, which is typically wound in a U-shape (or as a semicircle) as a single winding, with multiple turns.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of application Ser. No.11/068,592, titled “INDUCTION COIL DESIGN FOR PORTABLE INDUCTION HEATINGTOOL,” filed on Feb. 28, 2005, now U.S. Pat. No. 7,202,450 B2; which isa continuation of Ser. No. 10/800,540, titled “PORTABLE INDUCTIONHEATING TOOL FOR SOLDERING PIPES,” filed on Mar. 15, 2004, now U.S. Pat.No. 6,875,966 B1.

TECHNICAL FIELD

The present invention relates to induction heating equipment and isparticularly directed to an induction tool of the type which solders orbrazes metal pipe sections together. The invention is specificallydisclosed as an induction heating system in which a portable unitcontains an induction coil (a “work coil”) in a U-shaped orsemi-circular coil head configuration that allows a user to place thehead around an elongated object, such as a run of metal pipe sections,energize the work coil to solder two pipes sections together to form ajoint, and then to remove the head from the pipe run. The portable unitis available in various power ratings, and the more powerful portableunits can include a heat exchanger and a set of heat pipes to removethermal energy from the head.

The portable unit contains one or more power capacitors to sharereactive electrical current with the induction coil, to minimize theamount of current running through a cable from a power supply to theportable unit. The induction coil is made of Litz wire to minimize powerloss and thermal energy generation due to the skin effect of largerconductors; alternatively, the coil may be constructed of copper tubing,or the coil may comprise heat pipes that use a copper outer layer. Thecoil head includes heat pipes in some of the embodiments, and in theembodiments where the heat pipes do not carry the load current, thephysical proximity of the heat pipes to the (induction) work coil causesthe heat pipes to receive some of the magnetic field energy produced bythe work coil; when determining the physical placement of the heat pipesin this type of coil head, consideration is given to reducing orminimizing the magnetic flux received by the heat pipes.

The coil head includes an inner wall that is U-shaped or semi-circular,and an outer wall. Both types of walls should be at least somewhatabrasion-resistant and heat-resistant. The work coil windings arelocated between these two sets of walls, and the heat pipes (if theyextend into the coil head region) are also located within or betweenthese two sets of walls. The induction coil has a general racetrackconfiguration, which is typically wound between the U-shaped orsemi-circular inner wall and the outer wall as a single winding; thereare multiple turns which comprise adjacent conductors that stack up nextto one another to create a “wider” coil face. The dimensions of theinduction coil have a generally preferred characteristic as compared tothe dimensions of the workpiece pipe sections that are to be soldered orbrazed together, which is described below in greater detail.

The coil head can be made attachable to and detachable from theremainder of the portable unit at a mounting wall, to allow for heads ofvarious sizes and various power ratings to be interchangeably used inthe portable unit. The coil head can also be swivelable, if desired. Themounting wall and outer walls are heat-insulative in some embodiments(those with heat pipes running through the mounting wall into the head),and are somewhat heat-conductive in other embodiments (those with noheat pipes running into the head). The inner wall is typically thermallyinsulative, particularly at its surface that may come into contact witha workpiece being inductively heated.

The portable unit uses a finger-depressible trigger to actuate anelectrical switch, which initiates the “heating event” to make a solderjoint or a brazed joint. Alternatively, a foot switch could be used toinitiate the heating event, in which the foot switch is located outsidethe housing of the portable unit. As a further alternative, a differenttype of switching action could be utilized; for example, the portableunit could be attached to a robotic arm in an automatic manufacturingprocess control system, and the electrical switch could merely comprisea solid-state relay that is actuated by a remote computer. Or theportable unit could be actuated by a proximity sensor that detects thephysical proximity of the coil head to a predetermined type or mass oftarget material.

A power cable is typically mounted to the portable induction heatingtool, either as a “permanent” fixture, or via an electrical plug andreceptacle. If a receptacle is used, the power cable plugs into the backof the portable unit, away from the coil head. The power cable carrieselectrical power and electrical control signals to the portable unit. Analternative “receptacle” for receiving power is an antenna, in which thepower is received in the form of electromagnetic energy, and thus nopower cable is needed.

The work coil is typically more efficient in inductively heating acylindrical workpiece when the coil itself is configured in asemi-circular profile, so that it “wraps” around about half of thecircumference of the outer surface of the workpiece. If the inner wallis substantially “thin” then the work coil will exhibit an arcuate“length” that is just over one-half the circumference of the workpiece.The work coil is also typically more efficient in inductively heating acylindrical workpiece when the “thickness” of the work coil (i.e., thedistance between the inner and outer walls of the coil head) is aboutequal to the radius of the workpiece at its outer diameter dimension.

In a typical use of the heating tool of the present invention, two pipesections are brought together in a co-linear arrangement, and acylindrical coupler is slid over both pipe sections at the locationwhere they abut one another. A bonding material is made available tocreate a solid bond between the coupler and each of the pipe sections.The heating tool is brought into a proximal position to the coupler (itcan even make physical contact with the coupler), and the work coil isenergized, thereby heating the entire coupler and both sets of bondingmaterial, and thus melting the bonding material (assuming it issoldering or brazing compound), then de-energizing the work coil toallow the bonding material to solidify to form a hard bonding joint. (Inan alternative mode, the two pipe sections could be bonded directly attheir abutting ends, without the use of a coupler.)

BACKGROUND OF THE INVENTION

Induction heating devices have been available for many years, includingsome that raise the temperature of susceptors containing metallicsubstances that have eddy currents induced therein when receiving themagnetic field produced by a work coil of the induction heating device.Some of these induction heating devices have been used to connect twosections of pipe together; in some cases the induction heating devicessolder the pipe sections together, or even to weld the pipe sectionstogether, in certain high-powered induction devices.

One example induction heating device is disclosed in U.S. Pat. No.5,374,808 and is used with a “pull test” machine that has a stationarychuck and a moveable chuck that pulls apart two test pieces thatpreviously have been bonded together. The induction heating device has aU-shaped core or “pole piece” that consists of two spaced-apart oppositeends that define an air gap therebetween. An induction coil is wrappedaround the U-shaped pole piece, thereby forming an induction coil with amagnetic core. A capacitor is connected to opposite ends of theinduction coil to create a tank circuit, and a power oscillator can beused to adjust the power level and frequency of electrical energy thatis supplied to the tank circuit. In general, this induction heatingdevice is used to test the strength of two thermally non-conductive testpieces that have been bonded together. It is not being used to solder orweld two pieces together.

Another patent, U.S. Pat. No. 5,412,184, discloses an induction heatingtool that is shaped like a jaw-like cylinder. The jaws containelectrical conductors that provide inductive heat (as a magnetic field)when energized, and the jaws have a curved cross-section that brings thetwo edges of the jaw-like structure into contact after being wrappedaround a pipe or other cylindrical object that is to be heated. Thereare inner surface and outer surface conductors that are connected in amanner so that their current flows will be in opposite directions toreduce the electromagnetic radiation that is external to the device. Oneof the embodiments (see FIG. 7) uses a pistol grip to pull the jawstogether around the pipe to be heated.

Another patent, U.S. Pat. No. 5,350,902, discloses an induction heatingdevice that has a handle with a hollow interior, a “wrist” connected toone end of the handle, a U-shaped pole piece having two spaced-apartends, a tank circuit including an induction coil wrapped around the polepiece, and a capacitor connected to the induction coil. There is also a“head” connected to the wrist that includes a housing for receiving theU-shaped pole piece, in which the two spaced-apart ends of the polepiece extend outwardly beyond the housing. A susceptor is to be placedin juxtaposition to the ends of the U-shaped pole piece, and thesusceptor is heated by magnetic flux passing between the two ends of thepole piece. The wrist provides an articulating mount for the head, inwhich the wrist provides multiple degrees of freedom of motion so thehead can swivel about two joints, which are essentially ball and socketmembers.

U.S. Pat. No. 5,786,575 discloses a “wrap tool” that has first andsecond coil regions and flange regions for inducing oscillating magneticfields to fuse a plastic coupling to a substrate. The flange regions ofthe wrap tool open to receive a pipe, and then close to surround thepipe before a heating event, in which the pipes will be melted and fusedtogether.

U.S. Pat. No. 4,521,659 discloses an induction heating gun that can fusethermoplastics using an alternating current that passes through a tankcircuit, in which the inductor member of the tank circuit is wrappedaround a curved pole piece of a ferromagnetic material. The magneticflux in the induction coil flows to the ends of the pole piece and intoa screen placed between the materials to be joined, and the flux inducesa current in the screen which generates heat to melt the thermoplasticstogether.

U.S. Pat. No. 3,428,769 discloses an induction heating tool for weldingor brazing tubes, in which the heating tool has an overall shape of apliers-type tool that clamps around the tube to be heated. The clampingaction is by use of two separate jaws.

Published patent application number US 2003/0226838 A1 discloses amagnetic welder that provides an induction coil to heat a set of metalworkpieces sufficiently to form a weld bond. The induction coil has amovable element that, when “opened,” forms a gap to allow the coil to beplaced over the workpieces, and after the coil has been moved intoposition, the movable element “closes” to circumscribe the workpieces.The magnetic welder exhibits an insulated handle that includes a triggerthat actuates the magnetic field. The induction coil can also have alocking mechanism that may be used to lock the coil in its closedposition.

Some of the conventional inventions use flexible coil members to allowthe induction coil to be essentially “wrapped” around the workpiece, orto be bent into a desired shape with respect to a workpiece. Patentsdescribing such an arrangement include U.S. Pat. No. 6,346,690, U.S.Pat. No. 5,412,184 (noted above), U.S. Pat. No. 5,352,871, U.S. Pat. No.5,266,764, U.S. Pat. No. 5,113,049, U.S. Pat. No. 4,695,712, U.S. Pat.No. 4,388,510, and U.S. Pat. No. 3,260,792.

Others of the conventional inventions use coils that are liquid-cooled,in which the induction coil is hollow, and a cooling fluid is directedthrough the hollow coil to take heat away from the energized coil.Patents describing such an arrangement include U.S. Pat. Nos. 4,271,345and 3,365,563.

As noted above, there are several conventional inventions that use aninduction coil that “opens” to receive a workpiece (as a “side-entry”),and then “closes” to essentially surround the workpiece for the heatingevent. Other patents describing such an arrangement include U.S. Pat.No. 5,874,713, U.S. Pat. No. 5,786,575, and U.S. Pat. No. 3,365,563.

One variation if the conventional inventions is a side-entry inductioncoil, in which the coil itself does not necessarily move to allow aworkpiece to be inserted into a heating area or heating zone. However, a“flux concentrator” is provided at the mouth of the coil which is madeof ferrite material, and which is movable between a “loading” position(i.e., an open position) and a “heating position” (i.e., a closedposition). This arrangement is disclosed in U.S. Pat. No. 5,630,958.This arrangement is different than the movable coil inventions;nevertheless there is a movable magnetic circuit member that has an openposition and a closed (heating) position.

It would be an improvement to provide an induction heating tool that iscapable of soldering or brazing metal pipes together withoutforce-cooling liquid running through the induction coil conductors, oralternatively using heat pipes as the induction coil conductors, andmoreover by using a very portable induction heating tool in which theinduction coil is easily placed around portions of a cylindrical object(such as two pipes), without having to “wrap” or “close” the inductioncoil windings around the pipes, and without needing a separate magneticcircuit member to be moved from an open (loading) position to a closed(heating) position.

SUMMARY OF THE INVENTION

Accordingly, it is an advantage of the present invention to provide aninduction heating apparatus having an induction work coil located in acoil head to solder or braze together cylindrical metallic objects, suchas metal pipes, in which the coil head has a shape that allows easyinsertion around the pipe sections, and can be easily removed once thepipes have been joined.

It is another advantage of the present invention to provide an inductionheating apparatus in which an induction work coil is included in a coilhead that has a U-shape or semi-circular shape that can be easilyinserted around cylindrical objects such as pipes, and in which theelectrical energy is delivered to a tank circuit that includes the workcoil and a set of power capacitors, to lower the real AC electricalpower required for delivery to the portable unit.

It is a further advantage of the present invention to provide aninduction heating apparatus in which an induction work coil is made ofLitz wire or electrically-conductive tubing which runs into a coil head,as well as including heat pipes that run into the coil head and transferheat back to a heat exchanger, all of which is part of the portableinduction heating unit, and in which the load current for the inductioncoil is not carried by the heat pipes.

It is still a further advantage of the present invention to provide aninduction heating apparatus in which an induction work coil is made ofLitz wire or electrically-conductive tubing which runs into a coil head,as well as including heat pipes that run between a mounting wall and aheat exchanger, in which the coil head is attached to the mounting wall,and heat is transferred through the mounting wall to the heat pipes andto the heat exchanger, all of which is part of the portable inductionheating unit, and in which the load current for the induction coil isnot carried by the heat pipes.

It is yet a further advantage of the present invention to provide aninduction heating apparatus in which an induction work coil is made oneor more heat pipes that run into a coil head, in which the heat pipesboth transfer heat back to a heat exchanger and carry the load currentof the inductive coil itself, all of which is part of the portableinduction heating unit.

It is still another advantage of the present invention to provide aninduction heating apparatus in which a portable unit can be easilyplaced around a cylindrical object (such as a pipe), and which includesan induction work coil and power capacitor as a tank circuit, and whichalso includes a receiving area to receive electrical power to drive theinduction coil/power capacitor tank circuit, perhaps via an externalcable connected to an electrical receptacle.

It is still a further advantage of the present invention to provide aninduction heating apparatus in which a portable unit can be easilyplaced around a cylindrical object (such as a pipe), and which includesan induction work coil that exhibits a substantially semi-circularprofile such that it proximally surrounds about one-half of the outercircumference of the cylindrical object. When energized, the inductioncoil magnetically couples with the cylindrical object to raise itstemperature, and a proximal bonding compound is also raised intemperature to bond one portion of the cylindrical object with a secondportion of the cylindrical object. The profile of the induction workcoil can alternatively exhibit substantially a U-shape, while alsomagnetically coupling with the cylindrical object.

Additional advantages and other novel features of the invention will beset forth in part in the description that follows and in part willbecome apparent to those skilled in the art upon examination of thefollowing or may be learned with the practice of the invention.

To achieve the foregoing and other advantages, and in accordance withone aspect of the present invention, an induction heating apparatus isprovided, which comprises: (a) a head portion, comprising: (i) an outerwall, (ii) an inner wall, (iii) an induction coil disposed between theinner and outer walls, wherein: (iv) the inner wall forms an openinghaving substantially a U-shape as its interior surface, (v) theinduction coil comprises an electrical inductor, and (vi) the inner walland the outer wall are substantially rigid, and do not exhibit movableportions with respect to one another; and (b) a grippable portion,comprising: (i) an enclosure surface, (ii) an electrical switchingcircuit, (iii) a receiving area that receives power for energizing theinduction coil, and (iv) at least one electrical conductor to carry thepower between the induction coil and the receiving area.

In accordance with another aspect of the present invention, an inductionheating apparatus is provided, which comprises: (a) a head portion,comprising: (i) an outer wall, (ii) an inner wall, and (iii) aninduction coil disposed between the inner and outer walls, wherein theinner wall forms a surface exhibiting an opening that may be placed suchthat the inner wall partially surrounds a workpiece, and wherein theinduction coil comprises an electrical inductor; and (b) a grippableportion, comprising: (i) an enclosure surface, (ii) an electricalswitching circuit, (iii) a receiving area that receives power forenergizing the induction coil, (iv) at least one electrical conductor tocarry the power between the induction coil and the receiving area; and(v) at least one heat pipe for transferring thermal energy from the headportion.

In accordance with yet another aspect of the present invention, aninduction heating apparatus is provided, which comprises: (a) a headportion, comprising: (i) an outer wall, (ii) an inner wall, (iii) aninduction coil disposed between the inner and outer walls, wherein theinner wall forms an opening that may be placed so as to partiallysurround a workpiece, and wherein the induction coil comprises anelectrical inductor; (b) a grippable portion, comprising: (i) anenclosure surface, (ii) an electrical switching circuit, (iii) areceiving area that receives power for energizing the induction coil,(iv) at least one electrical conductor to carry the power between theinduction coil and the receptacle; and (c) a heat exchanger portion toassist in transferring thermal energy from the head portion.

In accordance with still another aspect of the present invention, a coilhead for an induction heating apparatus is provided, which comprises:(a) an outer member; (b) an inner member, the inner member having afirst arcuate surface along a first, inner side wall, and a secondarcuate surface along a second, outer side wall, the first and secondside walls being of a shape such that the inner member exhibits aprofile that is substantially semi-circular; and (c) an induction coildisposed between the inner and outer members, the induction coilcomprising an electrical winding of a racetrack configuration that issubstantially arcuate of a semi-circular profile, such that it issubstantially positioned along the second, outer side wall of the innermember; the induction coil exhibiting a length dimension along itssubstantially semi-circular profile, between a first end and a secondend of the induction coil; wherein: when the inner member is movedproximal to a cylindrical workpiece that is to be heated, in which thecylindrical workpiece exhibits a circumference dimension along its outersurface, the length dimension of the induction coil is of a distancethat is substantially one-half of the workpiece circumference dimension.

In accordance with a further aspect of the present invention, a coilhead for an induction heating apparatus is provided, which comprises:(a) an outer member; (b) an inner member, the inner member having aninner side wall and an outer side wall, the inner side wall forming anopening for receiving a workpiece; and (c) an induction coil disposedbetween the inner and outer members, the induction coil comprising anelectrical winding that runs substantially along the outer side wall ofthe inner member, the induction coil being formed substantially in aracetrack configuration; wherein the outer member at least partiallycovers the induction coil.

In accordance with a yet further aspect of the present invention, a coilhead for an induction heating apparatus is provided, which comprises:(a) an outer member; (b) an inner member, the inner member having aninner side wall and an outer side wall, the inner side wall forming anopening for receiving a workpiece; (c) an induction coil disposedbetween the inner and outer members, the induction coil comprising anelectrical winding that runs substantially along the outer side wall ofthe inner member; and (d) at least one heat pipe that runs into the coilhead.

Still other advantages of the present invention will become apparent tothose skilled in this art from the following description and drawingswherein there is described and shown a preferred embodiment of thisinvention in one of the best modes contemplated for carrying out theinvention. As will be realized, the invention is capable of otherdifferent embodiments, and its several details are capable ofmodification in various, obvious aspects all without departing from theinvention. Accordingly, the drawings and descriptions will be regardedas illustrative in nature and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings incorporated in and forming a part of thespecification illustrate several aspects of the present invention, andtogether with the description and claims serve to explain the principlesof the invention. In the drawings:

FIG. 1 is a perspective view in partial cross-section of a portableinduction heating tool, constructed according to the principles of thepresent invention, depicting a first embodiment of a relativelyhigh-powered unit that includes heat pipes and a heat exchanger.

FIG. 2 is a perspective view in partial cross-section from the oppositeside of the tool of FIG. 1.

FIG. 3 is a perspective view in partial cross-section of a portableinduction heating tool, constructed according to the principles of thepresent invention, depicting a second embodiment of a relativelylower-powered tool that includes heat pipes and a heat exchanger.

FIG. 4 is a perspective view in partial cross-section from the oppositeside of the tool of FIG. 3.

FIG. 5 is a perspective view of the coil head of the tool of FIG. 3,from the right and front of the coil head, with one of the outer wallsmissing to show details of the coil head.

FIG. 6 is a section view from the front of the coil head of the tool ofFIG. 3.

FIG. 7 is a top view of the coil head of the tool of FIG. 3.

FIG. 8 is a front elevational view of the entire tool of FIG. 3.

FIG. 9 is a top plan view of the entire tool of FIG. 3.

FIG. 10 is a right-side elevational view of the entire tool of FIG. 3.

FIG. 11 is a bottom plan view of the entire tool of FIG. 3.

FIG. 12 is a perspective view in partial cross-section of a portableinduction heating tool, constructed according to the principles of thepresent invention, depicting a third embodiment of a relativelylower-powered tool that includes heat pipes and a heat exchanger.

FIG. 13 is a perspective view in partial cross-section from the oppositeside of the tool of FIG. 12.

FIG. 14 is a perspective view in partial cross-section of a portableinduction heating tool, constructed according to the principles of thepresent invention, depicting a fourth embodiment of a relativelylower-powered tool that includes heat pipes and a heat exchanger.

FIG. 15 is a perspective view in partial cross-section from the oppositeside of the tool of FIG. 14.

FIG. 16 is a perspective view in partial cross-section of a portableinduction heating tool, constructed according to the principles of thepresent invention, depicting a fifth embodiment of a relativelylower-powered tool that includes a heat exchanger but no heat pipes.

FIG. 17 is a perspective view in partial cross-section from the oppositeside of the tool of FIG. 16.

FIG. 18 is a perspective view in partial cross-section of a portableinduction heating tool, constructed according to the principles of thepresent invention, depicting a sixth embodiment of a relativelylower-powered tool which includes no heat exchanger and no heat pipes.

FIG. 19 is a perspective view in partial cross-section from the oppositeside of the tool of FIG. 18.

FIG. 20 is a perspective view from the front and right side of the coilhead of the tool of FIG. 18, with one of the outer walls removed to showdetails of the coil head.

FIG. 21 is a perspective view from the front and right side of analternative coil head design, usable in the heating tool of the presentinvention, in which the induction coil itself comprises a heat pipehaving an electrically conductive outer casing (with an insulativecoating).

FIG. 22 is a top view of an alternative coil head design, usable in theheating tool of the present invention, in which the inner wall and coilprofiles are substantially semi-circular; and showing the coil headpartially surrounding a two-piece tubular workpiece (in cross-section)in position for being heated.

FIG. 23 is a perspective view from the rear and right side of the toolof FIG. 16, showing a receptacle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference will now be made in detail to the present preferred embodimentof the invention, an example of which is illustrated in the accompanyingdrawings, wherein like numerals indicate the same elements throughoutthe views.

Referring now to FIG. 1, a portable (or “hand-held”) inductive heatingtool that provides magnetic energy using an induction work coil isillustrated, generally designated by the reference numeral 10. The workcoil “head” is depicted at the reference numeral 20, and it includes anouter wall 22, an inner wall 24, a set of electrical conductors thatmake up the induction work coil at 34, and a set of heat pipes at 32.The coil head 20 is attached to a mounting wall member 60, which is thenfurther attached to a mid-portion 40 of the portable heating tool 10. Onthe other side of the mid-portion 40 is a heat exchanger portion of thetool, generally designated by the reference numeral 50.

In FIG. 1, the inner wall 24 exhibits a somewhat U-shaped appearance, ormore accurately, a half-oval shape. This wall's approximate shape willbe often referred to herein as a “U-shape,” even though it may not lookexactly like the letter U. (Note that some other embodiments describedbelow use an inner wall that has a more semi-circular appearance; inother words, the U-shape in some of the other embodiments is a veryshallow “U”. For purposes of this patent document, the term “U-shape”pertaining to an induction coil or to the inner wall of a coil head willinclude all of the shapes illustrated in the drawings, and theirequivalents, and specifically including the embodiments in which thecoil shape is closer to a semicircle than it is to a “U”—see, forexample, FIG. 22.)

The shape of the inner wall 24 is designed to be placed partially arounda cylindrical object, such as a pipe, and as such it can be easilyinserted about, and later removed from, a long length of two pipesections at a location where a joint is to be formed with the two pipesections. The tool 10 can thus be used to solder two pipe sectionstogether, or using different materials at a higher temperature, the tool10 can be used for brazing two pipe sections together. If the inner wallis of a material that can withstand a relatively high temperature (e.g.,about 260 degrees C. for soldering, or 800-900 degrees C. for brazing)at least momentarily, then the inner wall 24 can be designed of a shapeand dimension so as to directly make mechanical contact with theworkpiece (e.g., the pipe segments) during the heating event that willsolder or braze the segments together. This configuration is a preferredform of the present invention.

It should be noted that it is the inner surface of the inner wall 24that must be able to withstand the maximum temperatures of the heatingoperation, since the inner surface is the portion that will make directcontact with the workpiece. If the inner wall 24 is made of a layeredmaterial, then the innermost layer would typically exhibit the highesttemperature rating, and would typically comprise a thermal insulativematerial. The other layers of such a layered inner wall 24 could exhibitsomewhat lower temperature ratings, and could comprise materials thatare thermal conductors, if desired. Of course, the outermost surface ofthe inner wall 24 must still be able to withstand direct contact withthe induction coil 34, which will tend to be raised in temperature as itconducts current.

The induction coil 34 (sometimes referred to herein as a “work coil”)also is sized and shaped to partially surround the workpiece (e.g., theunjoined pipe sections), and when induction coil 34 is energized, itcauses the workpiece and the adjacent solder or brazing compound to beraised in temperature to a sufficient extent that the entirecircumferential area of a round workpiece is appropriately heated,thereby ensuring a good bond around the entire diameter of a round(cylindrical) set of pipe sections, for example. Induction coil 34 istypically an electrical inductor. It will be understood that an idealinductor comprises a pure inductance, with no resistance or capacitance;however, an actual inductor will exhibit some resistance andcapacitance, along with its main inductance property. The resistance ofthe induction coil causes certain power losses, which typically causeheat to be generated by the coil when electric current flowstherethrough. The heat created by these power losses is an importantfactor that should be accounted for in the design of a portableinduction heating tool, such as that of the present invention. This heatis typically dissipated by the tool's thermal management system, whichis discussed herein for the various disclosed embodiments.

The “front” face of the coil head is generally designated by thereference numeral 30, and includes a front face or surface for the outerwall 22, at the reference numeral 26, and a front face or surface forthe inner wall 24, at the reference numeral 28. On FIG. 1, the ends ofthe heat pipes 32 are visible for illustrative purposes, but thisarrangement would not be necessary, nor necessarily desirable, in anactual unit. While it typically would be desirable for the heat pipes 32to run up to the front faces 26 and 28, the ends of the heat pipes wouldnot necessarily be visible, assuming the front faces would exhibit acertain thickness that covers the ends of the heat pipes.

In general, the inner wall 24 and the outer wall 22 are substantiallyrigid in structure, and do not have movable portions that can be“opened” to place a workpiece within a circumferential area, and then“closed” to essentially constrain the workpiece within thatcircumferential area. Such movable coil structures are used in some ofthe conventional induction heating tools. On the other hand, if desiredit certainly would be possible to build the coil head 20 in a mannersuch that a portion of the induction coil 34 could pivot or otherwisephysically move with respect to other portions of the coil head 20 andstill accomplish the main function of the present invention. (Thisstatement is also true for the other embodiments described herein.)However, since the U-shaped induction coil 34 is shaped to partiallysurround a workpiece, such a movable portion of the coil head 20 is notreally necessary in the present invention, and the rigid walls 22 and 24can be made so that they are essentially non-movable with respect to oneanother.

The mid-portion 40 of the tool 10 includes an outer case 42, and atrigger-type actuator button at 44. The operator grasps the unit withhis or her hand around the mid-portion case 42, and can use his or herindex finger to actuate the trigger 44. An alternative to thehand-actuated trigger 44 is to provide a foot switch, for example, thatis wired into the tool 10. All versions of the portable tool describedherein could be made to operate in this manner, i.e., using a footswitch instead of the hand-actuated trigger 44.

A further alternative to the trigger 44 is to provide an automatic“start” switch that is controlled by an external process control system.In this configuration, the tool 10 could be mounted on a robotic arm,for example, as part of an automated manufacturing assembly line tosolder or braze pipe sections together, which could be incorporated intoa larger device (such as an automobile). When the robotic arm has beenplaced in a predetermined position, the assembly line's process controlsystem could activate a relay (e.g., a solid-state switch) within thetool 10, and a heating event (or heating cycle) could then be initiated.All versions of the portable tool described herein could be made tooperate in this manner.

A yet further alternative is to provide a proximity sensor 38 that couldbe mounted on the tool 10 at various locations—see FIG. 1 for examples.The tool 10 could be placed into a mode in which the heating event isautomatically initiated once the proximity sensor determines that a“target” material (e.g., two sections of metal pipe to be joined) hascome within a predetermined distance from the coil head 20. This type ofoperating mode may be more suitable to a non-human user environment,such as one in which the tool 10 is attached to a robotic arm, forexample. All versions of the portable tool described herein could bemade to operate in this manner.

The largest portion in physical size of the tool 10 is the heatexchanger portion 50, as seen in FIG. 1. The heat exchanger is coveredby a portion of the outer casing at 52, which includes a number ofventing slots 54. Within the heat exchanger is a large heat sink 56, andalso a small fan (not shown on FIG. 1).

In addition, there is a receiving area 70 in heat exchanger portion 50for receiving power, which could be an electrical receptacle that isused for plugging into an electrical cable (not shown on FIG. 1), or forwiring an electrical cable directly into the portable unit (i.e., tool10) through an opening on the housing 52. Alternatively, receiving area70 could perhaps comprise an antenna, for receiving power in the form ofelectromagnetic energy, such as radio waves or microwaves.

Referring now to FIG. 2, the inner components of the mid-portion 40 andthe heat exchanger portion 50 are visible. The trigger button 44actuates an electrical switch 48, and this arrangement can be seen onFIG. 2. The heat exchanger fan 58 is also visible in FIG. 2, and ismounted in close proximity to the large heat sink 56, which exhibits alarge number of protruding pins, which alternatively (or in combinationwith) could be a large number of fins or vanes.

Also within the mid-portion 40 is a set of power capacitors 46. Thesecapacitors 46 exchange electrical energy with the work coil 34, therebyallowing the electrical current flowing through a power cable (not shownon FIG. 2), to be minimized by having reactive electrical current sharedbetween the capacitors and the work coil. As can be seen in FIG. 2, theheat pipes 32 run from the front face area 30 of the coil head 20 allthe way back to the heat sink 56 within the heat exchanger portion 50 oftool 10.

There are several variations of this heating tool design, and many ofthem are illustrated in this patent document. For example, not allinductive tool units require heat pipes even though the heat pipes areuseful for transferring energy away from the work coil area to the heatexchanger, and are thus more necessary for higher-powered units that candeliver more inductive power to a pipe to be soldered or brazed.Similarly, the work coil itself may include a high number of smallwindings that comprise Litz wire, and the number of windings within thework coil head 20 would depend on the power output and shape of themagnetic field to be generated. One suitable type of Litz wire ismanufactured by New England Wire Company, their “type 2 Litz,” which has2625 strands that are each #42 AWG insulated wires. As is known in theart, Litz wire is capable of delivering fairly high frequency electricalalternating current while minimizing the “skin effect” that wouldtypically be found in electrical conductors of larger diameters.

An alternative type of electrical conductor for use in the inductioncoil 34 is copper tubing, or the coil may comprise heat pipes that use acopper outer layer. These alternative coil materials may be arranged ina physical pattern as illustrated in FIGS. 1 and 2, or in other shapes,as desired for creating an induction coil. This includes such coilpatterns as illustrated in other embodiments described herein. It willbe understood that other electrically conductive materials could be usedin the induction coil, rather than copper; of course, copper exhibitsboth good electrical and thermal conductive characteristics at arelatively low cost. However, the inventors contemplate the use ofalternative coil materials, even though this patent document generallyrefers to “copper” tubing or heat pipes having a “copper” outer skin.

The heat pipes 32 transfer energy from the work coil head 20 to the heatexchanger 50, as noted above. One suitable heat pipe is manufactured byThermacore, such as a copper/water heat pipe of four millimeter outerdiameter, and twelve inches in length. Such heat pipes are each capableof removing about sixty (60) watts of thermal energy at an operatingtemperature of 100° C. These heat pipes 32 are essentially hermeticallysealed; the liquid inside the heat pipe vaporizes at the “hot” end atthe coil head 20, and the heat is transferred down to the “cool” end atthe heat sink 56, where the vaporized liquid now condenses and flows asa liquid via capillary action through wick material within the heatpipe, back toward the hot end at the coil head 20. Of course, other heatpipe models made by Thermacore, or other heat pipes made by differentmanufacturers, could be used in the present invention.

One negative effect of using heat pipes made of copper is that they willbe somewhat heated by the magnetic energy that is produced by the workcoil 34, if the heat pipes are positioned in close proximity to the workcoil conductors. Therefore, it is better if the heat pipes are locatedin regions of the coil head 20 where they receive a minimal amount ofthe magnetic energy produced by the work coil 34. Some details ofsuitable locations are provided in later views, such as in FIGS. 5 and6.

The materials used in the coil head generally should be selected tohandle high temperature, and should be at least somewhat resistant toabrasion and chemicals. Certain types of ceramic materials are suitablefor many heating applications. One suitable material is MACOR™, or someother type of high temperature insulating material, such as a differenttype of ceramic material. This is particularly appropriate for the innerwall of the coil head, especially for the innermost surface of the innerwall 24. For other portions of the coil head 20, a morethermally-conductive material may be suitable, including for the outerwall 22. A suitable material is aluminum nitride.

In some of the embodiments disclosed herein, there are no heat pipesrunning through the mounting wall, and in those situations the materialsused in the outer walls of the work coil preferably are heat conductive.In that situation, a suitable material is aluminum nitride. The innerwall's inner surfaces typically should always be of a thermallyinsulative material (e.g., MACOR), and one with a sufficiently hightemperature rating to withstand direct contact with a heated workpiece(at least for momentary contact—i.e., for the heating event interval).

In general, the heat sink size and power rating are selected based uponthe overall power ratings for the heating tool 10, itself. For example,a tool that is to remove 200 watts of power would have a 200watt-capable heat sink. An aluminum heat sink would be of a suitablematerial, and a “pin-fin” style is a suitable type of heat sink. Manysuppliers manufacture this type of heat sink, and they are available asstock items from many distributors and manufacturers.

The fan in the heat exchanger 50 is also selected for the power level ofthe tool. For example, a 200 watt tool could use a fan that is 80×80×25millimeters in size, and rated at 10 watts of electrical powerconsumption. This would be a common fan used in many consumerelectronics. Other tool power ratings could use fans of other sizes. Itshould be noted that the first embodiment illustrated in FIGS. 1 and 2is designed to continuously remove 300 watts of power (in the form ofheat energy) from the work coil head 20 area. A 200 watt tool also isdisclosed herein, starting in reference to FIG. 3. These above numericwattage values are in reference to the tool's thermal energy dissipationcapacity, not the power output rating of the induction coil, which isreferred to herein as the quantity of power that is “delivered” to theworkpiece. A third power characteristic of the induction heating toolsdescribed herein is the amount of power losses within the inductioncoil; these are resistive losses that generate thermal energy accordingto the equation P=I²R, where I is current in amperes, R is resistance(of the coil) in ohms, and P is power in watts.

Other induction heating tools having a lower thermal transfer rating arealso disclosed herein, including 100 watt tools and 90 watt tools. Suchpower ratings noted herein are in reference to the amount of thermalenergy that can be continuously removed from the coil head by the tool'sthermal management system. A tool having a heat exchanger and a fan willgenerally be able to remove more thermal energy than a tool that doesnot have these features. A tool having heat pipes running into the coilhead will generally be able to remove more thermal energy than a toolthat does not have that feature.

It should be noted, however, that the induction heating tool 10 canactually deliver a much greater quantity of power to a workpiece thanthe tool's thermal management system can continuously dissipate. Forexample, the heating coil 34 is able to deliver a much higher amount ofpower, such as 600 watts, to a workpiece. In a preferred mode of thepresent invention, the heating of a workpiece is accomplished by placingthe workpiece as closely (or tightly) as possible to the U-shaped innerwall and coil region. The tool 10 is then activated and the workpiece isheated by induction. When the workpiece reaches the desired temperature(usually indicated by melting of the braze or solder), then the tool 10is shut off. This cycle is then repeated for each joint.

However, the work coil 34 is also “heated” during each heating cycle,not by induction, but due to resistive losses within the induction coil34 itself. For example, if the coil delivers about 600 watts of power tothe workpiece, if its resistive losses are 400 watts during the heatingevent, and if its thermal management system can continuously transfer300 watts away from the coil head 20, then its maximum duty cycle isabout 75%, and its efficiency is about 60%. These characteristics aredefined as follows:Coil Efficiency={Power delivered to the workpiece, divided by coillosses+power delivered to the workpiece}Maximum duty cycle={Thermal transfer rating, divided by coil losses}

In the above example, the coil efficiency is: {600 w/(400 w+600 w)}=60%.

In the above example, the maximum duty cycle is: {300 w/400 w}=75%.

The above 60% coil efficiency has been achieved in a working prototypeof the present invention, and with refinements, an even greaterefficiency should be possible. A coil efficiency of 50% should beachievable even if the design “rules” that are described below are notprecisely followed; in other words, variations in the coil shape, size,and construction will lead to different results, but are still animprovement over conventional induction heating designs, and still fallwithin the principles of the present invention.

If the coil losses are less than or equal to the tool's continuousthermal transfer rating, then the induction coil 34 may be continuouslyenergized, so long as there are no other constraints in the system. Theinduction coil 34 may be cooled to increase the continuous thermaltransfer rating. However, a continuous use of such a portable inductionheating tool is not usually necessary, nor may it even be desirable,since such a heating tool would likely be bulkier, and thus somewhatless “portable.”

Therefore, for many important uses, the coil of the induction heatingtool of the present invention will typically operate at a greater powerrating, such that its coil losses are greater than the continuousthermal transfer rating. It that situation, the heating tool 10 shouldobserve a cooling off period between activations (e.g., “heatingevents”). Of course, the induction coil 34 may be cooled to permitrepetitive joining operations to occur more quickly. In the aboveexample, the duty cycle was calculated at 75%, which represents theratio of operating time to heating event time. At this 75% duty cycle,the heating events could be repeated after a cooling (or “cool off”)interval of about one-third the heating time. The cool down periodbetween heating events allows the coil head 20 to reach an acceptabletemperature before its coil 34 is energized again. A temperature sensorcould be incorporated in the coil head (or near the coil head) to ensurethat the tool is not used again until the acceptable temperature hasbeen achieved.

Another feature of the present invention is that the work coils may beinterchangeable for use with different workpiece (pipe) sizes that areto be soldered or brazed, as well as can be interchangeable for use indifferent duty cycles. For example, a “standard” 600 watt work coil 34could be connected to a 100 watt rated induction tool, if desired. The100 watt tool would have not be able to remove thermal energy as quicklyas a 300 watt tool, for example, and it would likely need to remain offfor a time interval before its next use. If interchangeable coil headsare desired, however, special care should be taken for making electricalconnections for the Litz wiring (or copper tubing), and also for theheat pipes that may (or may not) run into the coil head area. If aparticular coil includes one or more heat pipes, then the heat pipesrunning through the grip portion 40 can be positioned so as to contactthe heat pipes in the coil head 20, at their butt ends. A thermallyconductive grease could be applied thereto when interchanging such coilheads, which would assist in lowering the thermal resistance to thistype of heat transfer circuit.

The interior separation dimension between the walls 24 of the U-shapedinner wall of the work coil 20 can be varied, and such differentspacings could be used for coil heads that have the same power ratings,or they could be for coils of different power ratings. Again, theinterchangeability of the tool and coil heads is a feature of thepresent invention, and would require commonality of electricalconnections and of heat pipe connections between the work coil 20 andits mounting wall 60, as a set of minimum criteria.

It will be understood that the heat pipes 32 are not generally designedto carry electrical current, at least not the “load current” that drivesthe induction coil 34. There may be some electrical current induced inthe metal (e.g., copper) walls of the heat pipes 32 because a portion ofthe heat pipes run into the coil head area 20, and are thus exposed tothe magnetic field produced by the induction coil 34. However, theseelectrical currents merely are by-products of the magnetic field—theyare AC eddy currents that are induced by the magnetic field. Thisembodiment of the present invention should not be confused with some ofthe prior art induction heating devices that use metal tubes to carrythe load current, and in which these metal tubes are force-cooled bywater or some other cooling fluid (e.g., by air, or other gasses orliquids) running through the interior regions of the hollow tubes. Inthese prior art devices, the metal tubes are also the induction coilitself. The heat pipes of this embodiment of the present invention arenot the induction coil; as will be seen in some of the later-describedembodiments herein, the heat pipes do not even run into the coil headarea (in certain embodiments), and moreover, in some embodiments thereare no heat pipes at all—but there is always an induction coil.

Note, however, that alternative embodiments of the present invention aredescribed herein which use heat pipes that do carry the induction coilload current. In that configuration, the heat pipes themselves exhibitan electrically conductive outer layer of material (e.g., copper) thatis insulated from the other structural elements of the heating tool, andthis outer layer of electrically conductive material comprises theinduction coil itself. Such an alternative embodiment is illustrated inFIG. 21, which is described below.

When joining two pipe sections using the tool 10, a flexible “tape” or“ribbon” of soldering compound can be placed around each of the pipesections (not shown), and a cylindrical coupler member typically ismoved into place around the two unjoined pipe sections. In one mode ofthe present invention, a piece of the solder tape (or ribbon) isintroduced between the coupler member and one of the pipe sections; or apiece of the solder tape (or ribbon) is introduced between the couplermember and each of the two pipes sections. In this mode, the solderribbon or tape is pre-positioned between the coupler and at least one ofthe pipes.

The entire coupler assembly can then be heated by the magnetic fieldgenerated by induction coil 34, thereby raising the temperature of bothsolder tapes (ribbons) to their melting point, and bond the coupler toboth of the pipe sections. The induction coil must be “wide” enough toemit a magnetic field along the entire surface of the coupler; or thetool 10 can be “brushed” back and forth along the length of the coupler,so as to alternately heat up both ends of the coupler to thereby raisethe temperature of the solder pieces on both ends. As an alternative,the tool 10 could be used to heat up only one end of the coupler at atime; in that scenario, the two solder tapes (ribbons) would each beheated to form a bond, only one at a time.

Alternatively, the solder can be introduced in the form of a “wire” ofsolder that is provided on a spool (as a “roll”), in which the solderwire is brought into the workpiece area to touch the pipe sections to bejoined to the coupler while they are being exposed to the magnetic field(and thus heated), such that the solder will flow around thecircumference of the cylindrical pipes by a wicking action. In thisalternative mode, the solder would not be pre-positioned before theheating event commenced. In general, the soldering applications willrequire flux to be introduced, either separately or as part of thesolder compound itself. The flux can be applied separately by the user.

If the pipe sections are to be brazed together (rather than soldered),again a flexible “tape” or “ribbon” of brazing compound can beintroduced (e.g., pre-positioned) around the pipe sections (not shown),and then the entire assembly (typically with a coupler) is heated by themagnetic field generated by induction coil 34. Alternatively, a wire ofbrazing compound can be introduced to the workpiece while it is beingexposed to the magnetic field. For brazing operations, there would be noneed for any separate flux compound. In addition, the brazing compoundgenerally must be raised to a greater temperature than typical solderingcompounds.

Referring now to FIG. 3, a 200 watt induction heating tool 100 isillustrated, having a coil head 120, a mid-portion 140, and a heatexchanger portion 150. Work coil 120 includes an induction coil 134,several heat pipes 132, an outer wall 122, and an inner wall 124. Workcoil 120 also has a “front face” area 130, in which the front surfacesof the coil head walls are at 126 for the outer walls 122 and at 128 forthe inner wall 124.

The coil head 120 mounts to a support wall structure 160, and is therebyconnected to the mid-portion 140. Mid-portion 140 has an outer casing142, and also includes a trigger button 144.

The heat exchanger portion 150 also exhibits an outer casing at 152,which includes multiple cooling slots or vents 154. The heat exchangerincludes a heat sink 156, and a fan (not shown on FIG. 3). There is alsoa receiving area 170 in heat exchanger portion 150 for receiving power,which could be an electrical receptacle that is used for plugging intoan electrical cable (not shown on FIG. 3), or perhaps another structurefor receiving or transferring power.

Referring now to FIG. 4, the fan 158 can now be seen, as being mated tothe heat sink 156, which has multiple fins for increased cooling effect.The mid-portion 140 also includes an electrical switch 148 that isactuated by the trigger 144; it also includes a set of power capacitors146 that exchange reactive current with the induction work coil 134.Some of the heat pipes 132 can also be seen as traveling through themid-portion 140.

The main difference between the second embodiment of FIGS. 3 and 4 andthe first embodiment of FIGS. 1 and 2 is that the second embodiment(e.g., a 200 watt heat transfer-rated unit) has fewer heat pipes 132,and has a smaller heat sink and fan, as compared to the larger (e.g.,300 watt) unit of FIGS. 1 and 2. The work coil 120 could have the samephysical size as the work coil 20, if desired, or it could be smaller inphysical size, to reflect the fact that it would typically run at alower power rating. Since there are fewer heat pipes 132, the rate ofheat transfer would theoretically be smaller for the second embodimentof FIGS. 3-4 (unless different heat pipes of a greater thermal transferrating were used).

Referring now to FIG. 5, the general configuration of the Litz wireconductors (or copper tubing) that make up the work coil 134 is betterillustrated, since the “near” outer side wall 122 has been removed forillustrative purposes. Moreover, one of the heat pipes 132 can also beseen without the near outer wall in the view, and this heat pipe 132extends through the support wall 160 and out toward the face 126 thatwould appear on FIG. 5 if the near outer wall 122 was visible. It shouldbe noted that, in the embodiment of FIG. 5, the induction coil 134 wouldgenerally not comprise one or more heat pipes, since a separate heatpipe 132 is provided.

FIG. 6 illustrates some further details of the coil head design for thehead 120, and shows the orientation between the electrical coils 134that are made of Litz wire (or copper tubing), and also the physicalpositioning of the heat pipes 132 with respect to the coil conductors134 and also the inner and outer coil head walls 122 and 124,respectively. As discussed above, if the heat pipes 132 are made of ametallic material, such as copper, then they will receive and besomewhat heated by the magnetic field produced by the work coil 134 whenit is energized. The physical orientations illustrated in FIG. 6 providean example of the orientation of the heat pipes 132 that will tend tominimize the effect of this heating due to the eddy currents that willbe generated in the copper heat pipes. The positioning of the heat pipeswith respect to the induction coil windings is a fairly important factorthat should not be overlooked in a coil head design.

FIG. 6 also makes visible a set of electrically insulative members 136that can be inserted between the upper and lower runs of the coilconductors 134, and between the inner and outer walls 124 and 122,respectively. While this area could be left empty, it is typicallybetter to include such inserts 136 if they are also made of a thermallyconductive material. One suitable material is aluminum nitride. Theseinserts can be used in all coil head embodiments of the presentinvention.

Referring now to FIG. 7, the work coil head 120 is illustrated from anangle that clearly shows the U-shape of the inner wall 124 of the head.The physical orientation of the work coil windings 134 is illustratedbetween the inner wall 124 and the outer wall 122. Also clearly visiblein FIG. 7 are the “front face” surfaces 126 and 128 of the inner andouter walls 124 and 122, respectively.

Referring now to FIGS. 8-11, the “200 watt” embodiment of FIGS. 3 and 4(i.e., designated by the reference numeral 100) is illustrated in side,front, top, and bottom views. In this exemplary design, the overalllength is approximately twelve inches, the overall height isapproximately nine inches, and the maximum width is about three andone-half inches. The outer width of the coil head 120 is just over twoinches in this exemplary embodiment. It should be noted that thesedimensions are based on prototype units, and production units have notyet been implemented as of the writing of this patent document.

A power cable 172 can be plugged into a receptacle at receiving area170, as seen in FIG. 10. The receptacle, of course, could be positionedat a different location than indicated (at 170) on the tool 100. Thepower cable 172, alternatively, could be “hard-wired” into the tool 100at the receiving area 170 (or at a different location on the tool 100).

Referring now to FIG. 12, a third embodiment of an induction heatingtool is illustrated, generally designated by the reference numeral 200.This heating tool 200 includes many of the same components that wereseen in the other embodiments described above and illustrated in FIGS.1-11, including a work coil head 220, a mid-portion 240, a heatexchanger portion 250, and a mounting wall 260 between the mid-portion240 and the coil head 220. In this embodiment 200, the heat exchanger250 is somewhat smaller than in the second embodiment illustrated inFIGS. 3 and 4, and there are also fewer heat pipes (as can be seen inFIG. 13), and thus this particular tool 200 will typically have a lowercontinuous power rating, such as 100 watts of heat transfer capability.

In the coil head 220, there is a set of induction coils 234, a set ofheat pipes 232, an outer wall on both sides at 222, and an inner wall224 that has a general U-shape. The front face area is designated by thereference numeral 230, and there is a front face surface 226 for theouter wall 222 and a front face surface 228 for the inner wall 224.

The mid-portion 240 has an outer casing 242, and includes a triggerbutton 244. The heat exchanger portion 250 has an outer casing at 252that exhibits several vents or slots 254. Heat exchanger 250 alsoincludes a heat sink 256, and includes a receiving area 270 forreceiving power, which could be an electrical receptacle that is usedfor plugging into an electrical cable (not shown on FIG. 12), or perhapsanother type of structure for receiving or transferring power.

FIG. 13 also shows this third embodiment 200, and the power capacitors246 and an ON-OFF switch 248 are illustrated within the mid-portion 240.There is a single heat pipe 232 that travels along each side of themid-portion 240, and this heat pipe 232 travels into the coil head 220(as noted above in reference to FIG. 12). The fan 258 is illustrated asbeing mounted next to the heat sink 256, within the heat exchangerportion 250.

Referring now to FIG. 14, a fourth embodiment induction heating toolgenerally designated by the reference numeral 300 is illustrated. Thistool 300 is approximately the same in overall size as the thirdembodiment heating tool 200, however, the heat pipes do not extend intothe coil head region, which is a coil head 320. In this configuration,the power rating would be somewhat less than for the third embodimentdesign illustrated in FIGS. 12-13 if the same sized components are usedfor both. Moreover, the materials used for the inner and outer walls ofthe coil head 320, as well as for a mounting support 360 wouldpreferably have somewhat better heat transfer qualities, and thus be atleast somewhat heat conductive. As noted above, aluminum nitride couldbe used in the coil head walls and wall support to conduct heat awayfrom the work coil 320.

The induction heating tool 300 includes a work coil 320, a mid-portion340, a heat exchanger portion 350, and a mounting wall 360 between thework coil 320 and the mid-portion 340. The coil head 320 includes a workcoil 334, which is surrounded by a U-shaped inner wall 324 and a set ofouter walls 322. A front face area 330 includes a front face surface 326for the outer walls 322, and a front face surface 328 for the inner wall324.

The mid-portion 340 includes an outer casing 342 and a trigger button344. Heat exchanger portion 350 has an outer casing 352 that exhibitsseveral slots or vents 354. There is also a receiving area 370 in heatexchanger portion 350 for receiving power, which could be an electricalreceptacle that is used for plugging into an electrical cable (not shownon FIG. 14), or perhaps another type of structure for receiving ortransferring power.

On FIG. 15, the power capacitors 346 and an ON-OFF switch 348 arevisible, as being included within the mid-portion 340. As can be seen inFIG. 15, there is a single heat pipe 332 on both sides as it runs downthe mid-portion to the heat exchanger. As noted above, in this fourthembodiment 300, the heat pipes 332 do not extend through the supportwall 360 and into the coil head 320. Therefore, it is desired for thecoil head walls 322 and 324 to have some heat conductive capabilities,and also for the mounting support wall 360 to be able to transfer heat,and thus have some heat conductive characteristics. This embodiment 300might have a power rating that is about 10% lower than a similar-sizedtool that allows the heat pipes to travel through the support wall intothe coil head. For example, this fourth embodiment 300 could be designedfor a 90 watt continuous heat transfer rating, as opposed to the example100 watt rating of the embodiment 200 illustrated in FIGS. 12-13.

It should be noted that the coil head 320 could be mounted so as to beswiveled if desired, particularly since no heat pipes extend into thecoil head itself in this embodiment. A U-joint, or other pivotablemounting structure, could be used at the mounting wall 360, for example.A special provision would be needed for the electrical conductors thatrun into the coil head 320 to be at least somewhat flexible, in thisswivelable alternative.

Referring now to FIG. 16, a fifth embodiment of an inductive heatingtool is generally designated by the reference numeral 400. This fifthembodiment includes a coil head 420, a heat exchanger portion 450, and a“far end” graspable portion 440. It can be easily seen that the heatexchanger portion 450 and the “far end” portion 440 have exchangedpositions as compared to the fourth embodiment 300 illustrated on FIGS.14-15.

The coil head 420 includes a work coil 434, an inner wall 424 that issubstantially U-shaped, a set of outer walls 422, and a front faceregion 430. Each of the walls of the coil head include a front facesurface, which is the surface 426 for the outer walls 422, and thesurface 428 for the U-shaped inner wall 424.

The heat exchanger 450 includes an outer casing 452 which exhibitsseveral slots or vents 454. The mounting or support wall between thecoil head 420 and the heat exchanger 450 is designated by the referencenumeral 460. The “far end” portion 440 includes an outer casing 442, andalso has a receiving area 470 for receiving power, which could be anelectrical receptacle that is used for plugging into an electrical cable(not shown on FIG. 16), or perhaps another type of structure forreceiving or transferring power.

Referring now to FIG. 17, the power capacitors 446 and an ON-OFF switch448 are visible in the portion 440. ON-OFF switch 448 is actuated by atrigger button 444. FIG. 17 also shows the heat exchanger's internalcomponents, which includes a heat sink 460 and a fan 458 that is mountedclose to the heat sink.

As can be seen in FIG. 17, this fifth embodiment 400 includes no heatpipes whatsoever, and to achieve a better power rating, the heatexchanger has been mounted against the support wall 460 to achieve abetter overall heat transfer characteristic by transferring heat awayfrom the coil head 420 more quickly. In this configuration, the supportwall 460 and the coil head surfaces are preferably at least somewhatheat conductive, so as to enable better heat transfer away from the coilhead 420. In this design, the heat transfer capability would beapproximately the same as in the fourth embodiment 300 that wasillustrated in FIGS. 14-15 (e.g., 90 watts).

Referring now to FIG. 18, a sixth embodiment of an induction heatingtool is illustrated, and is generally designated by the referencenumeral 500. This embodiment 500 includes a coil head 520 and agraspable “end portion” 540. Coil head 520 includes a generally U-shapedinner wall 524 and a set of outer walls 522, which end at a front faceportion 530. The outer walls 522 exhibit front face surfaces at 526,while the inner wall 524 exhibits front face surfaces at 528.

Coil head 520 mounts to a support wall 560 that mounts to the endportion 540. End portion 540 exhibits an outer casing 542 and a triggerbutton 544. The end portion 540 also has a receiving area 570 forreceiving power, which could be an electrical receptacle that is usedfor plugging into an electrical cable (not shown on FIG. 14), or perhapsanother type of structure for receiving or transferring power.

The receiving areas 70, 170, 270, 370, 470, and 570 as a group aretypically designed as receptacles to act as electrical connectors. Inone preferred mode of the invention, these receptacles could comprise arecessed area in the housing or enclosure of the portable unit, with anumber of protruding (or “male”) prongs that are designed to fit intomating “female” slots at one end of a power cable, or an “umbilical”cable (see FIG. 10). However, for added reliability and safety, it willbe understood that these receptacles could be eliminated entirely bypermanently connecting such a power cable to the portable induction coilunit at the receiving area (70, 170, 270, etc.). Of course, if the powercable is subjected to considerable wear (which seems likely on many jobsites), then a connecting-disconnecting mechanism such as the receptaclewould appear to be a useful design solution. In one mode of theinvention, the receptacle-power cable junction could be “locking” innature to prevent untimely disconnections.

One alternative configuration of the present invention would be tore-configure the power receiving areas 70, 170, 270, 370, 470, and 570to act as an antenna that could receive power in the form ofelectromagnetic energy, which then could be converted into electriccurrent, for example. In such an alternative configuration, some type ofpower converter circuit would be necessary to generate current at afrequency that can drive, or is resonant for, the tank circuit of theinduction coil and power capacitor(s) of the tool.

Referring now to FIG. 19, the power capacitors 546 and an ON-OFF switch548 are illustrated as being contained within the end portion 540. Ascan be seen in FIG. 19, there are no heat pipes, and moreover, there isno heat exchanger as such in this “basic unit” 500. This type of “basic”design would likely have the least power capability of any of thedesigns disclosed in this patent document, since without any heat pipesor a separate heat exchanger, the heat transfer rate from the coil head520 likely would be at a rather minimal extent as compared to some ofthe other embodiments described herein.

Referring now to FIG. 20, the “basic design” heating tool 500 isillustrated in a manner to show some of the details of the coil head520. The Litz wire coil (or copper tubing) windings for work coil 534are illustrated, and they pass through the support wall 560 into the endportion surrounded by the casing 542. The coil windings 534 are visiblebecause one of the outer walls 522 has been removed from this view(i.e., the “near” wall).

The face area 530 of the coil head 520 is easily seen in FIG. 20,including the frontal or “face” area 526 of the outer wall 522 and thefrontal or “face” area 528 of the inner wall 524. The overall U-shape ofthe inner wall 520 is also visible in this view. Some of the dimensioncharacteristics of the coil 534 and the coil head region are illustratedon FIG. 20. For example, the induction coil 534 that is illustrated inFIG. 20 has a winding arrangement that can be referred to as a“racetrack” configuration, in which a single winding is “wrapped” backand forth in an overall oval-type fashion. In FIG. 20, there are twolayers of the induction coil, and each layer has three turns ofoval-shaped electrical conductor, all of which make up the overallsingle winding of the work coil 534. The “width” dimension of thisracetrack coil configuration is given by the dimension 772 on FIG. 20,and a “gap” dimension between the innermost turn of the oval-shaped coilis illustrated by the dimension 770. Such a coil arrangement can also bereferred to as a “single start, multi-turn” coil. It will be understoodthat other methods of winding the induction coil 534 could be used toconstruct a usable work coil, while still falling within the principlesof the present invention.

The electrical insulators that make up the inner wall 524 and outer wall522 also have important dimensions; more specifically the inner wall 524will preferably be made as thin as possible, while still maintaininggood insulation characteristics with regard to electrical resistance,and also while exhibiting either thermal insulation or thermalsemi-conductive characteristics, depending on the type of configurationof the overall hand-held soldering tool. These considerations werediscussed above, as to whether the inner wall 524 would be thermallyinsulative or thermally conductive (or perhaps thermally“semi-conductive”). In any event, the thickness of the inner wall isillustrated as the dimension 774 on FIG. 20. These dimensions describedabove will be discussed in greater detail below.

Referring now to FIG. 21, a yet further embodiment of the heating toolis illustrated, in which the induction coil is comprised of a heat pipe,rather than being comprised of a “standard” electrical conductor (suchas Litz wire, or such as copper tubing with an insulative coating). Theheat pipe embodiment of FIG. 21 is generally designated by the referencenumeral 600, and would have a standard heating tool body (not shown inits entirety in this view), along with a casing 642 and some type ofactuation button 644. The coil head is designated by the referencenumeral 620, and includes a coil 634, which protrudes through a supportwall 660. There is also an outer wall 622 and an inner wall 624, inwhich one side (i.e., the “near” side) of the outer wall 622 is removed,so that the coil windings 634 are readily visible. FIG. 21 alsoillustrates the frontal area 630 of the coil head 620, including a frontface 626 of the outer wall 622, as well as a front face 628 of the innerwall 624.

In this embodiment 600 of FIG. 21, the induction coil 634 is made of aheat pipe that is wrapped in the racetrack coil arrangement (e.g., asingle start, multi-turn coil), in which this heat pipe is one that iscomposed of an outer metallic casing, such as a copper casing or coppertubular material, although the metal should be electrically insulated.In this configuration, the coil 634 will be more or less “self-cooled,”because the heat pipe device is one that automatically transfers heataway from its “hot end” toward its cooler end, by changes in phase. Asdiscussed above, at the “hot end” the liquid within the heat pipe isvaporized, and as a gas travels toward the “cool end” where the gaseousphase material condenses to become a liquid, and then in that liquidphase travels back toward the “hot end,” where the cycle is repeated.

It will be understood that the heating tool 600 could be made of the“basic design” configuration, in which there is no heat exchanger and nofan, or it could be built in a configuration in which either a fan isprovided on the other side of the support wall 660, or in which both afan and a heat exchanger are provided at the “far end” of the tool(which is not visible on FIG. 21).

Referring now to FIG. 22, a top view of an alternative coil head profileof the induction tool of the present invention is illustrated. This coilhead is generally designated by the reference numeral 720, and exhibitsan outer wall 722, an inner wall 724, as well as the induction coilitself at 734. In FIG. 22, the inner wall 724 has its inner surfacepartially surrounding a tubular workpiece 710, and showing that theinner wall 724 is capable of coming into direct mechanical contact withthe workpiece 710.

In most soldering or brazing operations, an outer coupler is used at thepipe joint. In FIG. 22, the coupler is designated at 710. The pipesection to be soldered or brazed is illustrated at 714. In general, theinner diameter of the coupler 710 is just barely greater than the outerdiameter of the pipe 714, so a good mechanical coupling is achieved,both before and after the pipe 714 and coupler 710 are joined together.In FIG. 22, the inner wall 724 exhibits a semi-circular profile. FIG. 22is showing the area of the coil head 720 in which the induction coil 734has its main winding wrapped around the outer surface of the inner wall724. For purposes of illustration, it is presumed that the coil 734 inFIG. 22 is wrapped in a manner similar to the work coils illustrated inFIG. 20, i.e., a racetrack-type configuration that is wrapped in twolayers, in which each layer comprises three turns of the coil materialitself. In FIG. 22, the inner layer is illustrated with its outermostturn at 790, its next inner (or middle) turn at 794, and its innermost“turn” at 796. All three of these “turns” wind around the outer surfaceof the inner wall 724, thereby forming a substantially semi-circularprofile, including at the apex 792 of this inner layer of the winding.

The outer layer of the coil 734 has its outermost turn illustrated at780, its middle turn at 784, and its innermost turn at 786. All three ofthese turns of the outer layer form a substantially semi-circularprofile, which has an apex at the reference numeral 782. If this coil734 is indeed constructed of a single winding, then it will beunderstood that all of the turns of both layers are electricallyconnected in series, thereby forming a single electrical winding of theinduction coil 734. The coil conductors also extend back toward thesupport wall 760, and these portions of the coil are illustrated at 736,as two parallel electrical conductors. Of course, the term “parallel” inthe previous sentence is referring to its mechanical structure, and itwill be understood that these portions 736 are electrically connected inseries, as they are all part of the single coil winding of the coil 734.

It will be understood that an alternative coil could easily beconstructed in which there is more than one parallel winding, and infact the coil of FIG. 22 could easily be manufactured with two parallelwindings (i.e., electrically in parallel), and in that situation theinner winding would comprise the inner layer (i.e., the coil turns 790,794, and 796) while the second winding could comprise the outer layer(i.e., the coil turns 780, 784, and 786).

The coil head 720 includes a coil face region 730, and this face region730 would have a frontal face or surface 726 for the outer wall 722, anda frontal face or surface 728 for the inner wall 724. As seen in FIG.22, the inner and outer walls 728 and 726, respectively, both extendsomewhat past the outermost dimensions of the coil 734, which areillustrated at 780 and 790 on FIG. 22. This is arranged so as to protectthe electrical conductors that make up the coil 734.

Some of the mechanical dimensions of the coil head 720 will now bediscussed. A diametrical line 712 is illustrated on FIG. 22 as runningthrough the center of the three concentric circles that make up theinner and outer diameters of the tubular workpiece 710 and 714. In apreferred embodiment of the present invention, the induction coil 734will be wrapped in a semi-circle that runs from one end of the coilwhere it intersects this diametrical line 712, to the other end of thecoil which again intersects the diametrical line 712 on the oppositeside of the workpiece 710, 714. However, if the coil 734 is wrapped inmore than one layer, and also if it is wrapped in more than one turn,then it is virtually impossible for every turn of the coil 734 to comeup to this diametrical line 712 and stop direction at that line.Therefore, in the example illustrated on FIG. 22, it is the middle turnof the (three-turn) layers that most centrally intersects thediametrical line 712, which comprises the middle turns 784 and 794. Ithas been found in prototypical induction heating coil devices that thissemi-circular profile for the induction coil 734 is a very efficientdesign for heating the tubular workpiece 710.

On FIG. 22, an arcuate dimension 776 is illustrated as being drawn alongthe outer surface of the inner wall 724. This outer wall dimension 776is illustrating a desired dimension for the coil 734, as it contacts theouter surface of the inner wall 724. This arcuate dimension is referredto herein as the “length” of the induction coil 734. Also illustrated onFIG. 22 is a dimension 774, which was also seen on FIG. 20, andrepresents the thickness of the inner wall 724.

In a preferred embodiment of the induction coil used in the heating toolof the present invention, the coil 734 is constructed in a racetrackconfiguration, and the dimensions of the coil 734 are selected tooptimize the heating of the workpiece. In general, the induction coil734 should be wrapped as close to the workpiece tube 710 as possible.This of course means that the insulating member that comprises the innerwall 724 should be constructed to be as thin as possible. The “length”of the coil (i.e., dimension 776 on FIG. 22) should be approximatelyhalf of the circumference of the outer surface of the tubular workpiece710, plus π times the thickness of the inner wall 724 (i.e., thethickness dimension 774). In this manner, the ends of the induction coil734 will essentially align with the centerline of the tubular workpiece(i.e., the diametrical line 712 on FIG. 22). It is not necessary forthese dimensional criteria to be precisely adhered to, and minoralterations can be made while still achieving good efficiency.

Other dimensional considerations important in the present inventioninclude the considerations of the “width” of the coil, as well as the“gap” of the coil. These are the dimensions 722 and 770, respectively,depicted on FIG. 20. The induction coil should substantially be as wideas the length of the section of the tubular workpiece that is to beheated. (This is the dimension 772 on FIG. 20.) The gap dimension ingeneral should be about half of the width dimension of the inductioncoil. Therefore, the dimension 770 should be about one-half of thedimension 772, with regard to the dimensions illustrated on FIG. 20. Asnoted above, it is not necessary for these dimensional criteria to beprecisely adhered to, and minor alterations can be made while stillachieving good efficiency.

The overall thickness of the induction coil 734 is a trade-off betweenthe inductive coupling to the tubular workpiece and the coil's resistivelosses. Good results in a prototype coil head have been obtained whenthe coil's thickness was approximately equal to the radius of thetubular workpiece that is to be heated. On FIG. 22, the coil “thickness”is a dimension 778, which is the distance between the inner surface ofthe outer wall 722 and the outer surface of the inner wall 724.

One prototypical coil that works well in heating metal pipes is one thatexhibited a width dimension of 1.7 inches, a gap dimension of 0.76inches, an inner wall (insulating member) thickness of 0.075 inches, anda coil “length” of 1.728 inches. The “target” (or workpiece) was acopper coupler having a 0.95 inch outer diameter and a linear dimensionof about 1.6 inches. The coupler surrounds a copper pipe, or twosections of copper pipe that are to be joined by a soldering process.The coil head having the above dimensions was capable of heating theentire coupler, and of forming two solder bonds simultaneously, onebetween each pipe section and the coupler. As can be seen, FIG. 22 isnot to scale, especially with respect to the dimensions given for theabove prototype; the inner wall 724 in particular is illustrated asbeing “thicker” than typical.

Referring now to FIG. 23, the heating tool 400 is depicted from the rearso as to show the electrical receptacle 470. As can be seen in thisview, a power cord 472 includes a plug 474 that can be connected intoreceptacle 470.

It will be understood that the coil head shape of all of the coil headsdisclosed in this patent document are designed for easy installationaround a rather lengthy pipe, and then after a soldering or brazingoperation has occurred, the coil head may be easily removed from thejoined pipe sections. This is for ease of use by plumbers orpipefitters, and is an advantage that is not enjoyed by all suchsoldering or brazing tools known in the prior art. It will also beunderstood that the exact dimensions of the coil head can be readilychanged for different pipe sizes (or different coupler sizes), withoutdeparting from the principles of the present invention. As describedabove, the dimensions of the induction coils have a generally preferredrelationship as compared to the dimensions of the workpiece to besoldered or brazed, however, the exact dimensions can vary significantlywhile still using other principles of the present invention.

It will be further understood that the embodiments illustrated in FIGS.1-22 could have further modifications thereto, and also various othercombinations of components and locations of components than illustratedin these drawings, all without departing from the principles of thepresent invention. In addition, other applications for this type ofinduction heating tool design can readily be found, while still fallingwithin the teachings of the present invention.

It will also be understood that the operating frequency of the loadcurrent that drives the induction coil (e.g., one of the coils 34, 134,234, 334, 434, 534, or 634) will be important with respect to a resonantfrequency exhibited by the tank circuit that includes the induction coiland the power capacitor (e.g., one of the capacitors 46, 146, 246, 346,446, or 546). If possible, the load current will be supplied at theactual resonant frequency, which is possible if an output poweroscillator is used that automatically drives this load current at thecircuit's resonant frequency. If the output current is not provided atthe actual resonant frequency, then the efficiency of the electricalcircuit will be reduced. Certain pulse power output circuits can drivetank circuits at a very low frequency, almost down to DC (zero Hertz).

The present invention can work well at various operating frequencies,essentially as low as 10 Hertz up to as high as visual lightfrequencies. A more preferred range of operating frequencies is from afew kHz up to 2 MHz, inclusive; a yet more preferred range of operatingfrequencies is from 10 kHz through 300 kHz, inclusive; and a still morepreferred range of operating frequencies is from 50 kHz through 300 kHz,inclusive.

It will be understood that the present invention can well operatewithout the inclusion of a power capacitor (e.g., one of the capacitors46, 146, 246, 346, 446, or 546) within the hand-held portion of anoverall induction heating system. The inclusion of the capacitor has abeneficial effect, of course: that of minimizing the total currentrunning between the induction coil and the capacitor, which allows for asmaller electrical conductor for that run of wiring. The inclusion ofthe capacitor also has a detrimental effect: it increases the cost ofthe hand-held unit, and more weight is added to the hand-held unit,along with an increased space needed to enclose the capacitor(s). Itmust be said, however, that the inclusion of such a power capacitorusually provides more benefit than detriment.

It will further be understood that the present invention is not limitedto any particular type of soldering compound (with or withoutself-contained flux), or any particular type of brazing compound, andthus is not limited to any particular operating temperature for theheating events. Moreover, the bonding compound used in joining pipes, orother longitudinal objects, does not necessarily have to be comprised ofa soldering or brazing compound; certain hi-temperature epoxies could bequickly cured using the heating (and bonding) tool of the presentinvention.

All documents cited in the Detailed Description of the Invention are, inrelevant part, incorporated herein by reference; the citation of anydocument is not to be construed as an admission that it is prior artwith respect to the present invention.

The foregoing description of a preferred embodiment of the invention hasbeen presented for purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed. Any examples described or illustrated herein are intended asnon-limiting examples, and many modifications or variations of theexamples, or of the preferred embodiment(s), are possible in light ofthe above teachings, without departing from the spirit and scope of thepresent invention. The embodiment(s) was chosen and described in orderto illustrate the principles of the invention and its practicalapplication to thereby enable one of ordinary skill in the art toutilize the invention in various embodiments and with variousmodifications as are suited to particular uses contemplated. It isintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

1. A coil head for an induction heating apparatus, said coil headcomprising: (a) an outer member; (b) an inner member, said inner memberhaving an inner side wall and an outer side wall, said inner side wallforming an opening fbr receiving a workpiece; and (c) an induction coildisposed between said inner and outer members, said induction coilcomprising an electrical winding that runs substantially along saidouter side wall of said inner member, wherein said induction coil is aprimary source of thermal energy for heating said workpiece; furthercomprising: at least one external heat pipe that runs into said coilhead at a location different than at said opening for the workpiece,wherein said heat pipe tends to transfer thermal energy away from saidinner side wall of said inner member, and away from said opening; andwherein said heat pipe is not the primary source of thermal energy forheating the workpiece.
 2. The coil head as recited in claim 1, whereinsaid induction coil has a length dimension that extends substantiallyalong the electrical winding run along said outer side wall of the innermember, and exhibits one of the following shapes: (a) substantially aU-shape when viewed from a direction that is substantially perpendicularto said length dimension of the induction coil; and (b) substantially asemi-circular shape when viewed from a direction that is substantiallyperpendicular to said length dimension of the induction coil.
 3. Thecoil head as recited in claim 2, wherein: (a) said induction coil has awidth dimension that runs substantially perpendicular to said lengthdimension, and (b) wherein said induction coil comprises at least oneindividual turn having an outer dimension that is less than or equal tosaid width dimension in a direction that is substantially perpendicularto said length dimension.
 4. The coil head as recited in claim 1,wherein: (a) said induction coil has a first thickness dimension thatrepresents a distance between said outer side wall of the inner memberand an inner side wall of said outer member, (b) said induction coilcomprises at least one individual turn that is disposed within saidfirst thickness dimension between the inner and outer members; and (c)said at least one heat pipe also is disposed between said inner andouter members.
 5. The coil head as recited in claim 4, wherein alocation of said at least one heat pipe is disposed in at least one of:(a) between a surface of said outer side wall of the inner member and asurface of said inner side wall of said outer member, (b) within a slotin said inner member; and (c) within a slot in said outer member.
 6. Thecoil head as recited in claim 4, wherein a location of said at least oneheat pipe is selected so as to relatively minimize an effect of amagnetic field emitted by said induction coil upon an electricallyconductive portion of said at least one heat pipe.
 7. The coil head asrecited in claim 1, wherein said at least one heat pipe is interspersedwith at least one turn of the electrical winding of said induction coil.8. The coil head as recited in claim 1, wherein said induction coil isformed substantially in a racetrack configuration.
 9. The coil head asrecited in claim 8, wherein said outer member at least partially coverssaid induction coil.
 10. The coil head as recited in claim 9, whereinsaid inner member is made of a temperature-resistant material thatallows it to come into direct contact with said workpiece while saidworkpiece is being heated.
 11. The coil head as recited in claim 1,further comprising a heat sink; wherein said heat pipe comprises atubular structure that is hermetically sealed, and has a first endproximal to said coil bead and a second, opposite end proximal to saidheat sink, said heat pipe containing a liquid that substantiallyvaporizes at said first end as it is heated by said coil head, saidliquid then transferring heat toward said second end, where said liquidsubstantially condenses.
 12. The coil head as recited in claim 11,wherein said heat pipe includes a wick material within said hermeticallysealed tubular structure, and said condensed liquid flows, from saidsecond end toward said first end, by way of a capillary action throughsaid wick material.
 13. A coil head for an induction heating apparatus,said coil head comprising: (a) an outer member; (b) an inner member,said inner member having an inner side wall and an outer side wall, saidinner side wall forming an opening for receiving a workpiece; and (c) aninduction coil disposed between said inner and outer members, saidinduction coil comprising an electrical winding that runs substantiallyalong said outer side wall of said inner member; Her comprising: atleast one external heat pipe that runs into said coil head, wherein saidheat pipe tends to transfer thermal energy away from said inner sidewall of said inner member, and away from said opening; wherein: (d) saidinduction coil has a width dimension that runs substantiallyperpendicular to said length dimension; (e) said induction coilcomprises at least one individual turn having an outer dimension that isless than or equal to said width dimension in a direction that issubstantially perpendicular to said length dimension; (f) said inductioncoil has a length dimension that extends substantially along theelectrical winding run along said outer side wall of the inner member,and exhibits one of the following shapes: (i) substantially a U-shapewhen viewed from a direction that is substantially perpendicular to saidlength dimension of the induction coil; and (ii) substantially asemi-circular shape when viewed from a direction that is substantiallyperpendicular to said length dimension of the induction coil; (g) saidinduction coil has a width dimension that runs substantiallyperpendicular to said length dimension, and said induction coilcomprises at least one individual tarn having an outer dimension that isless than or equal to said width dimension in a direction that issubstantially perpendicular to said length dimension; (h) said inductioncoil has a first thickness dimension that represents a distance betweensaid outer side wall of the inner member and an inner side wall of saidouter member; and (i) said induction coil comprises a plurality ofindividual turns that are arranged in at least one of the followingconfigurations: (i) the individual turns are layered within said firstthickness dimension between the inner and outer members, such that saidfirst thickness dimension is greater than a second thickness dimensionrepresenting a thickness an electrical conductor of a single of saidindividual turns; and (ii) the individual turns are wound such that theylie alongside one another within said first thickness dimension betweenthe inner and outer members, and the first thickness dimension issubstantially the same as said second thickness dimension representing athickness an electrical conductor of a single of said individual turns.14. A method for heating a workpiece, using an induction heatingapparatus, said method comprising: (a) providing a coil head having: (i)an outer member, (ii) an inner member, said inner member having an innerside wall and an outer side wall, said inner side wall forming anopening for receiving a workpiece; (iii) an induction coil disposedbetween said inner and outer members, said induction coil comprising anelectrical winding that runs substantially along said outer side wall ofsaid inner member, wherein said induction coil is a primary source ofthermal energy for heating said workpiece; (b) providing at least oneexternal heat pipe that runs into said coil head at a location differentthan at said opening for the workpiece; (c) placing said inner side wallproximal to said workpiece; (d) energizing said induction coil togenerate a magnetic field that induces eddy currents in an electricallyconductive portion of said workpiece, and thereby raising a temperatureof said workpiece; and (e) transferring, by use of said heat pipe,thermal energy away from said inner side wall of said inner member, andaway from said opening, wherein said heat pipe is not the primary sourceof thermal energy for heating the workpiece.
 15. The method as recitedin claim 14, wherein said heat pipe comprises a tubular structure thatis hermetically sealed, and has a first end proximal to said coil headand a second, opposite end proximal to a heat sink, said heat pipecontaining a liquid that substantially vaporizes at said first end as itis heated by said coil head, said liquid then transferring heat towardsaid second end, where said liquid substantially condenses.
 16. Themethod as recited in claim 15, wherein said heat pipe includes a wickmaterial within said hermetically sealed tabular structure, and saidcondensed liquid flows, from said second end toward said first end, byway of a capillary action through said wick material.
 17. The method asrecited in claim 14, wherein: said workpiece is substantiallycylindrical in shape, and said cylindrical workpiece exhibits alongitudinal axis; said induction coil has a length dimension thatextends substantially along the electrical winding along said outer sidewall of the inner member, said induction coil has a width dimension thatruns substantially perpendicular to said length dimension, and furthercomprising the step of: (e) heating a longitudinal portion of saidcylindrical workpiece to an extent along said longitudinal axis that issubstantially equal to said width dimension of the induction coil.
 18. Amethod for heating a workpiece, using an induction heating apparatus,said method comprising: (a) providing a coil head having: (i) an outermember; (ii) an inner member, said inner member having an inner sidewall and an outer side wall, said inner side wall forming an opening forreceiving a workpiece; (iii) an induction coil disposed between saidinner and outer members, said induction coil comprising an electricalwinding that runs substantially along said outer side wall of said innermember; (b) providing at least one external heat pipe that runs intosaid coil head; (c) placing said inner side wall proximal to saidworkpiece; (d) energizing said induction coil to generate a magneticfield that induces eddy currents in an electrically conductive portionof said workpiece, and thereby raising a temperature of said workpiece;and (e) transferring, by use of said heat pipe, thermal energy away fromsaid inner side wall of said inner member, and away from said opening;wherein: said workpiece is substantially cylindrical in shape, and saidcylindrical workpiece exhibits a longitudinal axis; said induction coilhas a length dimension that extends substantially along the electricalwinding run along said outer side wall of the inner member, saidinduction coil has a width dimension that runs substantiallyperpendicular to said length dimension, and further comprising the stepof: (f) heating a longitudinal portion of said cylindrical workpiece toan extent along said longitudinal axis that is substantially equal tosaid width dimension of the induction coil; and wherein said cylindricalworkpiece comprises: a cylindrical coupler of a first outer diameter anda first inner diameter, and a first longitudinal length; a firstcylindrical pipe section of a second outer diameter; a secondcylindrical pipe section of a third outer diameter, which issubstantially equal to said second outer diameter; wherein said firstinner diameter of the coupler is at least as large as said second andthird outer diameters of the first and second pipe sections; and andfurther comprising the steps of: (g) substantially abutting said firstand second pipes sections together such that their longitudinal axes aresubstantially co-linear, (h) placing said coupler over both said firstand second pipe sections; (i) introducing a bonding compound betweensaid coupler and at least one of the first and second pipe sections; (j)placing said coil head at a position proximal to said coupler, and (k)energizing said induction coil to heat said coupler and said bondingcompound, thereby forming a bond between said coupler and said at leastone of the first and second pipe sections.
 19. The method as recited inclaim 18, wherein said induction coil width dimension is greater than orequal to said first longitudinal length of the coupler, thereby allowingsaid induction coil to simultaneously heat the entire coupler.
 20. Themethod as recited in claim 19, wherein said induction coil has athickness dimension that represents a distance between said outer sidewall of the inner member and an inner side wall of said outer member;and said coil thickness dimension is substantially equal to a radius ofsaid workpiece along its outer diameter.